1. Field of the Invention
The present invention relates to a driving apparatus for a plasma display panel (hereinafter called xe2x80x9cPDPxe2x80x9d) of a matrix display type.
2. Description of the Related Background Art
Various studies have been made on PDPs which are thin flat display devices, and one of those PDPs is a matrix display type of PDP.
FIG. 1 is a diagram showing the constitution of a driving apparatus for the matrix display type of PDP.
In FIG. 1, row electrodes Y1 to Yn and row electrodes X1 to Xn, each pair of which corresponds to a single one of rows of one screen (the first row to the n-th row), are formed on a PDP 1. Column electrodes D1 to Dm which correspond to the respective columns of one screen (the first column to the n-th column) are formed perpendicular to those row electrodes each with an unillustrated dielectric layer and discharge space provided in between. Each discharge cell corresponding to a single pixel is formed at the intersection of one pair of row electrodes and a single column electrode.
An address driver 2 converts pixel data of individual pixels based on a video signal to pixel data pulses DP1 to DPn whose voltage values correspond to the logic levels of the individual pieces of the pixel data, and applies the pixel data pulses to the column electrodes D1-Dm row by row. A row-X electrode driver 3 generates a reset pulse for initializing the amount of the residual wall charges of each discharge cell and a discharge sustain pulse for maintaining the discharge state of each light-emitting discharge cell to be discussed later, and applies those pulses to the row electrodes X1-Xn.
A row-Y electrode driver 4, like the row-X electrode driver 3, generates reset pulses each for initializing the amount of the residual wall charges of the associated discharge cell and discharge sustain pulses each for maintaining the discharge state of each light-emitting discharge cell, and applies those pulses to the row electrodes Y1-Yn. The row-Y electrode driver 4 also generates priming pulses for reforming the charge particles that are generated in individual discharge cells and scan pulses each for producing charges whose amount corresponds to the pixel data pulse in the associated discharge cell to thereby set a light-emitting discharge cell or a non-emitting discharge cell, and applies those pulses to the row electrodes Y1-Yn.
FIG. 2 shows the specific constitutions of the row-X electrode driver 3 and the row-Y electrode driver 4 with respect to an electrode Xj and an electrode Yj. The electrode Xj is the j-th one of the electrodes X1-Xn and the electrode Yj the j-th one of the electrodes Y1-Yn. The part between the electrodes Xj and Yj serves as a capacitor C0.
The row-X electrode driver 3 is equipped with two power supplies B1 and B2. The power supply B1 provides a voltage Vs1 (for example, 170 V), and the power supply B2 provides a voltage Vr1 (for example, 190 V). The positive terminal of the power supply B1 is connected via a switching element S3 to a connection line 11 for the electrode Xj, with the negative terminal grounded. A switching element S4 is connected between the connection line 11 and the ground, and a series circuit of a switching element S1, a diode D1 and a coil L1 and a series circuit of a coil L2, a diode D2 and a switching element S2 are both connected via a capacitor C1 to the ground. The end of the diode D1 on that side of the capacitor C1 serves as an anode, and the end of the diode D2 on that side of the capacitor C1 serves as a cathode. The positive terminal of the power supply B2 is connected via a switching element S8 and a resistor R1 to the connection line 11, with the negative terminal grounded.
The row-Y electrode driver 4 is equipped with four power supplies B3 to B6. The power supply B3 provides a voltage Vs1 (for example, 170 V), the power supply B4 provides a voltage Vr1 (for example, 190 V), the power supply B5 provides a voltage Voff (for example, 140 V) and the power supply B6 provides a voltage Vh (for example, 160 V; Vh greater than Voff). The positive terminal of the power supply B3 is connected via a switching element S13 to a connection line 12 for a switching element S15, with the negative terminal grounded. A switching element S14 is connected between the connection line 12 and the ground, and a series circuit of a switching element S11, a diode D3 and a coil L3 and a series circuit of a coil L4, a diode D4 and a switching element S12 are both connected via a capacitor C2 to the ground. The end of the diode D3 on that side of the capacitor C2 serves as an anode, and the end of the diode D4 on that side of the capacitor C2 serves as a cathode.
The connection line 12 is connected via a switching element S15 to a connection line 13 for the positive terminal of the power supply B6. The power supply B4 has a positive terminal grounded and a negative terminal connected via a switching element S16 and a resistor R2 to the connection line 13. The power supply B5 has a positive terminal connected via a switching element S17 to the connection line 13 and a negative terminal grounded.
The connection line 13 is connected via a switching element S21 to a connection line 14 for the electrode Yj. The negative terminal of the power supply B6 is connected via a switching element S22 to the connection line 14. A diode D5 is connected between the connection lines 13 and 14. A series circuit of a switching element S23 and a diode D6 is also connected between the connection lines 13 and 14. The end of the diode D5 on that side of the connection line 14 serves as an anode, and the end of the diode D6 on that side of the connection line 14 serves as a cathode.
The on/off actions of the switching elements S1-S4, S8, S11-S17 and S21-S23 are controlled by a control circuit (not shown). The arrows at the individual switching elements in FIG. 2 indicate terminals for control signals from the control circuit.
In the row-Y electrode driver 4, the power supply B3, the switching elements S11-S15, the coils L3 and L4, the diodes D3 and D4 and the capacitor C2 constitute a sustain driver portion, the power supply B4, the resistor R2 and the switching element S16 constitute a reset driver portion, and the remaining power supplies B5 and B6, switching elements S13, S17, S21 and S22 and diodes D5 and D6 constitute a scan driver portion.
The operation of the PDP driving apparatus with the above constitution will now be explained with reference to a timing chart in FIG. 3. The operation of the PDP driving apparatus consists of a reset period, an address period and a sustain period.
First, in the reset period, the switching element S23 in the row-Y electrode driver 4 is set on. The switching element S23 becomes an on state both in the reset period and sustain period. At the same time, the switching element S8 in the row-X electrode driver 3 is turned on and the switching element S16 in the row-Y electrode driver 4 is turned on. The other switching elements are off. The on state of the switching element S8 causes a current to flow from the positive terminal of the power supply B2 to the electrode Xj through the switching element S8 and the resistor R1, and the on state of the switching element S16 causes a current to flow from the electrode Yj to the negative terminal of the power supply B4 through the diode D5, the resistor R2 and the switching element S16. The potential of the electrode Xj gradually increases at the rate specified by the time constant of the capacitor C0 and the resistor R1 and becomes a reset pulse RPx, and the potential of the electrode Yj gradually decreases at the rate specified by the time constant of the capacitor C0 and the resistor R2 and becomes a reset pulse RPy. The reset pulses RPx are simultaneously added to the respective electrodes X1-Xn, and the reset pulses RPy are generated for the respective electrodes Y1-Yn and are simultaneously added to the respective electrodes Y1-Yn.
The simultaneous addition of those reset pulses RPx and RPy causes all the discharge cells of the PDP 1 to be excited and discharged, generating charge particles, and a predetermined amount of wall charges are evenly formed in the dielectric layers of the entire discharge cells after the discharging is finished.
After the levels of the reset pulses RPx and RPy are saturated, the switching elements S8 and S16 are turned off before the reset period ends. At the point of time, the switching elements S4, S14 and S15 are turned on, causing both the electrodes Xj and Yj to be grounded. As a result, the reset pulses RPx and RPy disappear.
When the address period starts, the switching elements S14 and S15 are turned off, the switching element S23 is turned off and the switching element S17 is turned on at which time the switching element S22 is turned on. The on action of the switching element S17 renders the power supplies B5 and B6 in a series-connected state, so that a negative potential indicating the difference between the voltages Vh and Voff appears on the negative terminal of the power supply B6 to be applied to the electrode Yj.
In the address period, the address driver 2 converts pixel data of individual pixels based on a video signal to pixel data pulses DP1 to DPn whose voltage values correspond to the logic levels of the individual pieces of the pixel data, and sequentially applies the pixel data pulses to the column electrodes D1-Dm row by row. As shown in FIG. 3, pixel data pulses DPj and DPj+1 are respectively applied to the electrodes Yj and Yj+1.
The row-Y electrode driver 4 sequentially applies priming pulses PP of a positive voltage to the row electrodes Y1-Yn. The row-Y electrode driver 4 also sequentially applies scan pulses SP of a negative voltage to the row electrodes Y1-Yn immediately after the application of the respective priming pulses PP and in synchronism with the respective timings of the pixel data pulses DP1 to DPn.
With regard to the electrode Yj, in generating the priming pulse PP, the switching element S21 is turned on and the switching element S22 is turned off. The switching element S17 stays on. Consequently, the potential Voff on the positive terminal of the power supply B5 is applied as the priming pulse PP to the electrode Yj via the switching element S17 and then the switching element S21. After the application of the priming pulse PP, the switching element S21 is turned off and the switching element S22 is turned on both in synchronism with application of the pixel data pulse DPj from the address driver 2. As a result, the negative potential on the negative terminal of the power supply B6 which indicates the difference between the voltages Vh and Voff is applied as the scan pulse SP to the electrode Yj. In synchronism with the timing at which the application of the pixel data pulse DPj from the address driver 2 is stopped, the switching element S21 is turned on and the switching element S22 is turned off, causing the potential Voff on the positive terminal of the power supply B5 to be applied to the electrode Yj via the switching element S17 and then the switching element S21. Thereafter, as in the case of the electrode Yj, the priming pulse PP is likewise applied to the electrode Yj+1, and the scan pulse SP is applied to the electrode Yj+1 in synchronism with application of the pixel data pulse DPj+1 from the address driver 2, as shown in FIG. 3.
In the discharge cells related to the row electrode to which the scan pulses SP have been applied, those discharge cells to which the pixel data pulses of a positive voltage have also been applied at the same time discharge and most of the wall charges will be lost. Since no discharging occurs in those discharge cells which have been applied with the scan pulses SP but not the pixel data pulses of a positive voltage, the wall charges remain. At the time, the discharge cells in which the wall charges have remained become light-emitting discharge cells while those from which the wall charges have disappeared become non-emitting discharge cells.
At the transition from the address period to the sustain period, the switching elements S17 and S21 are turned off and the switching elements S14 and S15 are turned on instead. The switching element S4 maintains its on state.
In the sustain period, the on state of the switching element S4 in the row-X electrode driver 3 sets the potential of the electrode Xj nearly to the ground potential of 0 V. When the switching element S4 is turned off and the switching element S1 is turned on, the charges stored in the capacitor C1 cause the current to reach the electrode Xj via the coil L1, the diode D1 and the switching element S1 and flow into the capacitor C0, charging the capacitor C0. At the time, the potential of the electrode Xj gradually increases as shown in FIG. 3 due to the time constant of the coil L1 and the capacitor C0.
Then, the switching element S1 is turned off and the switching element S3 is turned on. Consequently, the potential Vs1 on the positive terminal of the power supply B1 is applied to the electrode Xj. Then, the switching element S3 is turned off and the switching element S2 is turned on, causing the current to flow into the capacitor C1 from the electrode Xj via the coil L2, the diode D2 and the switching element S2 because of the charges stored in the capacitor C0. At the time, the potential of the electrode Xj gradually decreases as shown in FIG. 3 due to the time constant of the coil L2 and the capacitor C1. When the potential of the electrode Xj reaches nearly 0 V, the switching element S2 is turned off and the switching element S4 is turned on.
Through the above operation, the row-X electrode driver 3 applies a discharge sustain pulse IPx of a positive voltage as shown in FIG. 3 to the electrode Xj.
At the same time the switching element S4 is turned on at which the discharge sustain pulse IPx disappears, the switching element S11 is turned on and the switching element S14 is turned off in the row-Y electrode driver 4. When the switching element S14 is on, the potential of the electrode Yj is nearly the ground potential of 0 V; however, when the switching element S14 is turned off and the switching element S11 is turned on, the charges stored in the capacitor C2 cause the current to reach the electrode Yj via the coil L3, the diode D3, the switching element S11, the switching element S15, the switching element S13 and the diode D6 and flow into the capacitor C0, charging the capacitor C0. At the time, the potential of the electrode Yj gradually increases as shown in FIG. 3 due to the time constant of the coil L3 and the capacitor C0.
Then, the switching element S11 is turned off and the switching element S13 is turned on. Consequently, the potential Vs1 on the positive terminal of the power supply B3 is applied to the electrode Yj. Then, the switching element S13 is turned off and the switching element S12 is turned on, causing the current to flow into the capacitor C2 from the electrode Yj via the diode D5, the switching element S15, the coil L4, the diode D4 and the switching element S12 because of the charges stored in the capacitor C0. At the time, the potential of the electrode Yj gradually decreases as shown in FIG. 3 due to the time constant of the coil L4 and the capacitor C2. When the potential of the electrode Yj reaches nearly 0 V, the switching element S12 is turned off and the switching element S14 is turned on.
Through the above operation, the row-Y electrode driver 4 applies a discharge sustain pulse IPy of a positive voltage as shown in FIG. 3 to the electrode Yj.
Since the discharge sustain pulses IPx and IPy are alternately generated and are alternately applied to the respective electrodes X1-Xn and the electrodes Y1-Yn in the sustain period, as apparent from the above, the light-emitting discharge cells where the wall charges remain repeat discharge emission and maintain the light-emitting state.
The conventional PDP driving apparatus is constructed in such a way that the scan driver portion uses a PMOS FET or NMOS FET as the switching element S21 and uses an NMOS FET as the switching element S22, with the node of the series circuit of those switching elements serving as the output to the electrode Yj. In the case, as the on-state resistance of the FET that constitutes the switching element S21 is high, the driving performance becomes considerably poorer than that of the FET that constitutes the switching element S22. Because it is impossible to supply the discharge sustain pulse current from the sustain driver to the electrode Yj via the switching element S21 during the sustain period, the discharge sustain pulse current is supplied to the electrode Yj of the PDP through the bypass circuit that has the switching element S13. The scheme undesirably leads to a larger circuit scale and a cost increase.
Accordingly, it is an object of the present invention to provide a PDP driving apparatus which is capable of supplying a discharge sustain pulse current to a PDP during the sustain period without increasing the circuit scale.
A PDP driving apparatus according to the present invention, which drives a plasma display panel having plural pairs of row electrodes and a plurality of column electrodes laid perpendicular to the pairs of row electrodes, forming discharge cells at respective intersections of the pairs of row electrodes and the column electrodes, comprises a scan driver for supplying a scan pulse to one of each of the pairs of row electrodes to select a light-emitting discharge cell and a non-emitting discharge cell; and a discharge sustain driver for supplying a discharge sustain pulse to one of each of the pairs of row electrodes to maintain light emission of only the light-emitting discharge cell. The scan driver includes two switching elements having one ends commonly connected to one of each of the pairs of row electrodes in such a way that when the scan driver is activated, a first potential is applied to the other end of one of the two switching elements and a second potential lower than the first potential and equal to a potential of the scan pulse is applied to the other end of the other switching element. The output of the discharge sustain driver is electrically connected to the other end of the other switching element when the discharge sustain driver is activated.
According to the present invention, the discharge sustain pulse output from the discharge sustain driver is supplied to one of each pair of row electrodes via the other switching element.
A PDP driving apparatus according to the present invention, which drives a plasma display panel having plural pairs of row electrodes and a plurality of column electrodes laid perpendicular to the pairs of row electrodes, forming discharge cells at respective intersections of the pairs of row electrodes and the column electrodes, comprising a sustain driver for supplying a discharge sustain pulse to one of each of the plural pairs of row electrodes to permit only a light-emitting discharge to maintain light emission; and a scan driver for supplying a scan pulse to one of each of the pairs of row electrodes to select a light-emitting discharge cell and a non-emitting discharge cell. A drive current from the sustain driver flows in the same path in the scan driver at a charging time and a discharging time.